Autopilot swaying left and right of track



  • So most of you probably already noticed that the autopilot instead of holding the track cleanly is actually swaying left and right around the track. This happens in NAV and OMNI mode no matter if you're on VLOC following a VOR radial or on GPS.

    It always goes a minute or so off to one side, then makes a steeper turn and overshoots the track to the other side, and repeats that behavior.
    swaying.PNG

    There were discussions already if this behavior is simply trying to replicate the real world Autocontrol IIIB behavior since it seems not as precise, but I would like to know if that is really intentional.
    If it's not, maybe it's something to be fixed in the upcoming update.

    Here are some real pilots talking about deficiencies of the Autocontrol IIIB:
    https://www.piperowner.org/talk/discussion/comment/164318/#Comment_164318

    The only time my autopilots “hunts” (does S-turns along the track) instead of tracking solidly is when there’s been a rapid temperature drop and condensation has formed inside the plane.

    Since I don't like the swaying left and right, I copied the STICKANDRUDDER PIDs in ai.cfg from the G36 to the PA-28R and the autopilot is now holding the track steadily.


  • JF Staff

    This is something we are trying to improve as part of our other FDE changes. The MSFS AP behaviour changed with the recent sim update and has been challenging to work with but we'll take a look at the PID suggestion.



  • I've experienced this too, though I'm not sure if it's like that in the real aircraft. Interestingly, it doesn't happen when tuned to a VORTAC (at least the one I used yesterday, IIU) which I guess makes sense as they are meant to be more accurate.



  • @Martyn said in Autopilot swaying left and right of track:

    This is something we are trying to improve as part of our other FDE changes. The MSFS AP behaviour changed with the recent sim update and has been challenging to work with but we'll take a look at the PID suggestion.

    Thanks for the quick response, glad that it was not entirely intentional 🙂
    I was quite lazy by copying all the PIDs from the stock G36, but then again, there's not much to do wrong with it since the AP behaves quite nicely with it.
    I'm sure there's just a few of the PIDs actually relevant for this behavior.



  • @copper, can you post the changes you made to correct this issue?



  • @RetiredMan93231 said in Autopilot swaying left and right of track:

    @copper, can you post the changes you made to correct this issue?

    Sure:
    Go to the ai.cfg of the G36:

    Official\OneStore\asobo-aircraft-bonanza-g36\SimObjects\Airplanes\Asobo_Bonanza_G36\ai.cfg

    and copy the whole [STICKANDRUDDER] section (all the lines below it) from there and paste it into the ai.cfg of the addon:

    Community\justflight-aircraft-pa28-arrow-iii\SimObjects\Airplanes\JF_PA28_Arrow\ai.cfg

    replacing the [STICKANDRUDDER] section there.

    I did not notice any negative side effects during numerous flights. I cannot judge if the behavior of the autopilot is now realistic or not, but I basically just need it to follow whatever I set it up to and that works fine.



  • @copper Thank you sir! I followed your suggestion to copy some ai.cfg settings from the stock Bonanza and it helped considerably. I am now able to fly an ILS approach including procedure turns using a combination of heading mode to manage the procedure turn and then switching to localizer normal mode when inbound on a 30 degree intercept to the localizer course. Its now as close to real life as anyone could reasonably expect and I have no hesitations using it to keep my instrument skills sharp. Using the Bonanza AI stick&rudder parameters, the autopilot captured and followed the localizer as good as real life down to minimums for the approach.



  • @copper this worked great! Thanks!



  • Replacing the entire AI.CFG file with the one from the G36 seems to also work well...

    And, making the following changes to the AI.CFG file will smooth out the Heading Hold and Altitude Hold...

    headingPID = 1.0, 0.01, 1.0, 0.2, 1.0
    verticalSpeedPID = 1.0, 0.05, 0.2, 300.0,1000.0



  • @RetiredMan93231 So the "smooth" heading hold means that it will also no longer be swaying left and right?
    Then I'd use your parameters instead of the G36 ones since those don't fix the vibration of Altitude Hold unfortunately.



  • @copper said in Autopilot swaying left and right of track:

    @RetiredMan93231 So the "smooth" heading hold means that it will also no longer be swaying left and right?
    Then I'd use your parameters instead of the G36 ones since those don't fix the vibration of Altitude Hold unfortunately.

    I recommend doing both, because the G36 AI.CFG fixes the VOR/LOC tracking... Start with the G36 file, then add my additional fixes to the G36 file.

    I don't see any pitch vibration after making these changes, but if you still have pitch vibration, you can also try adding this @weptburrito fix to the pitchPID parameters... https://community.justflight.com/post/8010



  • @copper Thanks for the tips this morning. Have made the changes and are looking forward to the improvements.

    Happy flying...



  • Here are some additional recommended changes that will further improve the autopilot performance...

    ai.cfg

    [STICKANDRUDDER]
    ;pitchPID = 2.0, 0.1, 5.0, 1.0, 100.0
    pitchPID = 2.0, 0.1, 2.0, 1.0, 100.0

    ;headingPID = 2.0, 0.01, 1.2, 0.2, 1.0
    headingPID = 1.0, 0.01, 1.0, 0.2, 1.0

    ;verticalSpeedPID = 0.5, 0.01, 0.35, 300.0,1000.0
    verticalSpeedPID = 1.0, 0.05, 0.2, 300.0,1000.0

    ;nav_yawPID = 0.015, 0.005, 0.001, 1.0, 360

    systems.cfg

    [AUTOPILOT]
    yaw_damper_gain =0 ;2



  • @RetiredMan93231 said in Autopilot swaying left and right of track:

    Here are some additional recommended changes that will further improve the autopilot performance...

    ai.cfg

    ;nav_yawPID = 0.015, 0.005, 0.001, 1.0, 360

    I notice that you didn't include a replacement for this line. Just checking to confirm whether that is what you intended.



  • It would generally be great to have a full STICKANDRUDDER section. Is your change based on the stock or on the G36 values?



  • @Sender46 said in Autopilot swaying left and right of track:

    @RetiredMan93231 said in Autopilot swaying left and right of track:

    Here are some additional recommended changes that will further improve the autopilot performance...

    ai.cfg

    ;nav_yawPID = 0.015, 0.005, 0.001, 1.0, 360

    I notice that you didn't include a replacement for this line. Just checking to confirm whether that is what you intended.

    Yes, this line has been commented out to completely remove this parameter...

    This change, and the change to the Yaw Damper parameter, are needed to eliminate a constant left rudder input coming from the autopilot that causes the aircraft to slip during cruise flight. This aircraft has no autopilot rudder axis, so no rudder input should occur from the autopilot.



  • @copper said in Autopilot swaying left and right of track:

    It would generally be great to have a full STICKANDRUDDER section. Is your change based on the stock or on the G36 values?

    I am using the complete AI.CFG file from the G36 as the basis for these changes...



  • @copper Thanks so much for this suggestion which worked perfectly for me too.



  • @copper said in Autopilot swaying left and right of track:

    It would generally be great to have a full STICKANDRUDDER section. Is your change based on the stock or on the G36 values?

    Here is the full [STICKANDRUDDER] section of the AI.CFG file...

    [STICKANDRUDDER]
    rudderGroundPID = 0.015, 0.001, 0.001, 1.0, 1.0 ; Pk,Ik,Dk,I boundary, D boundary
    throttleGroundPID = 1.0,0.10,10.0,10.0,20.0
    brakeDifferentialPID = 0.0, 0.0,0.0,0.0, 0.0
    throttleDifferentialPID = 0.0 ,0.0,0.0,0.0,0.0
    throttlePID = 20.0,0.50,20.0,20.0,500.0
    ;pitchPID = 2.0, 0.1, 5.0, 1.0, 100.0
    pitchPID = 2.0, 0.1, 2.0, 1.0, 100.0
    rollPID = 1.2, 0.1, 0.6, 8.0, 100.0
    ;headingPID = 2.0, 0.01, 1.2, 0.2, 1.0
    headingPID = 1.0, 0.01, 1.0, 0.2, 1.0
    ;verticalSpeedPID = 0.5, 0.01, 0.35, 300.0,1000.0
    verticalSpeedPID = 1.0, 0.05, 0.2, 300.0,1000.0
    nav_ex1PID = 3.5, 0.1, 10.0, 0.035, 50.0
    ;nav_yawPID = 0.015, 0.005, 0.001, 1.0, 360
    glideSlopePID = 4.12, 0.05, 4.5, 2.0, 60.0
    flightLevelPID = 100.0, 1.0, 10.0, 100.0, 1000.0



  • @RetiredMan93231 said in Autopilot swaying left and right of track:

    @Sender46 said in Autopilot swaying left and right of track:

    @RetiredMan93231 said in Autopilot swaying left and right of track:

    Here are some additional recommended changes that will further improve the autopilot performance...

    ai.cfg

    ;nav_yawPID = 0.015, 0.005, 0.001, 1.0, 360

    I notice that you didn't include a replacement for this line. Just checking to confirm whether that is what you intended.

    Yes, this line has been commented out to completely remove this parameter...

    This change, and the change to the Yaw Damper parameter, are needed to eliminate a constant left rudder input coming from the autopilot that causes the aircraft to slip during cruise flight. This aircraft has no autopilot rudder axis, so no rudder input should occur from the autopilot.

    Great explanation. Thank you.